An Israeli study published December 8 in the New England Journal of Medicine reveals that a booster (third) shot of the Pfizer-BioNTech Covid-19 vaccine at least five months after the second dose reduced the risk of death from the disease by 90 percent in people over age 50.

Researchers from Clalit Health Services, Ben-Gurion University of the Negev and Sapir Academic College drew their conclusion from an analysis of patient data from Clalit, Israel’s largest national HMO.

A total of 843,208 participants met the eligibility criteria, of whom 758,118 (90%) received the booster during the 54-day study period, during which the incidence of Covid-19 in Israel was one of the highest in the world due to the Delta variant.

“Among those who received a [third] shot, a 90% reduction in COVID morality was observed – 88% among men and 94% among women – compared to those who received only two doses,” the researchers wrote.

“Although this study is observational in nature, we believe that the significant findings and the observed potential for saving many lives could assist decision makers in assessing the benefit of providing the booster to broad populations, especially persons 50 years of age or older,” they concluded. “However, studies with longer-term follow-up periods to assess the effectiveness and safety of the booster are still warranted.”